When using some types of photographic film in space, it is desirable that the film be provided with an inert, humidified atmosphere. This is especially true of specialized film such as that used in the Wide Field Cameras aboard the Astro-1 Shuttle Mission scheduled to be launched by NASA. This film is of the type used for photographing diffuse sources of ultraviolet radiation and has an emulsion which requires a selected range of relative humidity in order to prevent it from being adversely affected or possible ruined. For providing such an environment, a camera canister is constructed having provisions adapted to regulate temperature and pressure of the interior of the canister within a selected range. As relative humidity changes with variations of temperature and pressure, it is necessary to keep the range of temperature within a range which, at a depressed temperature, will not cause saturation and condensation of the water vapor within the canister, and which, at an elevated temperature, will not cause a condition which is too dry for the film. Likewise, pressure of the canister must be regulated to prevent a condition from occurring which is too humid or dry. In this instance, an increase of pressure causes the relative humidity to increase proportionally, and a decrease of pressure causes a proportional decrease of relative humidity. The upshot of this is that not only must the canister containing the film and camera be temperature and pressure regulated, but the atmosphere used to charge the canister prior to flight must be generated at a pressure which approximates that of the pressure of the canister while it is in use. Further, the atmosphere used to charge the canister may not be pressurized and stored in a pressure bottle or vessel because, for a given relative humidity, the pressure at which saturation and condensation of the water vapor occurs therein is prohibitively low. This means, for example, that if a gas mixture having a relative humidity of 20% at one atmosphere (14.7 PSI) is stored or shipped in a pressure bottle, it can be pressurized to no more than five atmospheres (73.5 PSI) before saturation and condensation of the water vapor will begin.
Accordingly, it is an object of the present invention to provide an apparatus which enables a sealed canister containing cameras and film to be charged with a selectively humidified inert gas, with a high degree of control being established over the quantity of water vapor provided to the gas mixture and the pressure of the mixture. Further, this invention also provides a convenient way to charge the canister with a leak-revealing gas so that it may be inspected for leaks and for purging the canister of leak-revealing gas prior to charging with the water vapor/inert gas mixture.